cDNA cloning, expression and immune function analysis of a novel Rac1 gene (AjRac1) in the sea cucumber Apostichopus japonicus

Identification of a novel RhoA gene in the sea cucumber Apostichopus japonicus and its immune regulatory function via interacting with miR-2012-5p

RhoA (Ras homolog A) protein is a representative member of the Rho GTPase family and is involved in various cellular processes. The function of RhoA in sea cucumbers is unclear. In this study, we hypothesized that RhoA may regulate the innate immune response of Apostichopus japonicus. Our data showed that 1) the complete sequence of RhoA from A. japonicus (named AjRhoA) was 968 bp, with a high level sequence conservation across the echinoderms and other phyla; 2) tissue expression analysis showed that AjRhoA transcripts and protein exhibited higher abundance in coelomocytes, whereas the relative expression of miR-2012-5p was lower in coelomocytes; 3) interactive binding sites and a negative regulatory targeting relationship between AjRhoA and miR-2012-5p were confirmed through a dual-luciferase reporter assay and functional validation in vivo; 4) the relative expression levels of AjRhoA transcripts and protein were upregulated in coelomocytes 4- and 72-hour post infection (hpi) with Vibrio splendidus, whereas miR-2012-5p was expressed in the opposite pattern; 5) both AjRhoA silencing and miR-2012-5p overexpression suppressed the phagocytic capacity of A. japonicus compared with the control at 4 and 72 hpi. Our observations suggest that AjRhoA can regulate the pathogen-induced immune response of A. japonicus through the "AjRhoA-miR-2012-5p" module during the early infection, while miR-2012-5p plays a direct immunomodulatory role as the infection progresses.

Characterization of small GTPase Rac1 and its interaction with PAK1 in crayfish Procambarus clarkii

Ras-related C3 botulinum toxin substrate 1 (Rac1) participates in many biological processes. In this study, a Rac1 gene was identified in the crayfish Procambarus clarkii with an open reading frame of 579 bp that encoded 192 amino acids. This predicted 21.4 kDa protein was highly homologous to those in other invertebrates. Real-time PCR analysis revealed that Pc-Rac1 was expressed in all examined tissues with the highest expression level in hemocytes. The transcriptional expression level of Pc-Rac1 was significantly upregulated in hemocytes and hepatopancreas after lipopolysaccharide (LPS) or polyinosinic: polycytidylic acid (poly I: C) induction. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western blot analysis suggested that a recombinant Pc-Rac1 protein was successfully expressed in E. coli. Far-western blot analysis demonstrated that Rac1 can interact with the PBD domain of p21-activated kinase 1 (PAK1). RNA interference of Pc-Rac1 affected the mRNA expression levels of immune-related genes lectin, Toll, crustin, TNF, ALF and cactus. These results suggest that Pc-Rac1 is involved in the innate immune responses in P. clarkii.